1. Field of the Invention
This invention relates to the heat treatment of cobalt base alloys for use at elevated temperatures.
2. Description of the Prior Art
This invention relates to a heat treatment for a specific cobalt base alloy. This cobalt alloy is disclosed in U.S. Pat. application U.S. Ser. No. 638,882 now U.S. Pat. No. 4,078,922 on which a Notice Of Allowance was mailed on Oct. 5, 1977. The subject matter of this allowed United States patent application is expressly incorporated herein by reference. This allowed United States patent application contains claims directed at the alloy in two forms, compositions suitable for the production of cast parts and compositions suitable for the production of wrought parts. The present invention relates to a heat treatment which is useful in the connection for the production of wrought parts. The alloy composition range suitable for the production of wrought parts is presented in Table I which shows broad and preferred ranges from allowed application Ser. No. 638,882, now U.S. Pat. No. 4,078,922 and a preferred composition for use in conjunction with the heat treatment of the invention. This alloy is unique since the protective film which forms in service and prevents further surface attack is based on alumina rather than chromia film which is found in virtually all other cobalt superalloys. The composition of this alloy differs from the composition of other known alloys and consequently its heat treatment would not be expected to be similar to heat treatments employed with prior art alloys.
TABLE I ______________________________________ Most Broad Preferred Preferred ______________________________________ Cr 18-27 18-25 18-23 Ni+Fe 10-20 13-17 13-17 (1) W+Mo 8-12 8-10 8-10 (2) Ta+Cb 2-14 2-4 2-4 (3) C .25-.45 .25-.45 .25-.45 Al 3.5-5.0 3.7-4.6 4.2-4.6 Hf .5-2.0 .5-2.0 .5-2.0 Ti 0-.5 0-.5 0-.5 Y .02-.07 .02-.07 .02-.07 B 0-.5 0-.5 0-.5 Co Bal Bal Bal ______________________________________ (1) Ni only (2) W only (3) Ta only
The monograph entitled "Cobalt Base Superalloys 1970," published by the Cobalt Information Center in 1970, contains a brief summary of the heat treatment supplied to cobalt base superalloys. Briefly, these conventional heat treatments usually involve a solution heat treatment at a temperature in excess of 2000.degree. F. followed by an optional aging treatment at a lower temperature to produce precipitation of a desired phase. The aging treatments employed range from about 1200.degree. to about 1500.degree. F.